Molecular dynamics and the glass transition in a columnar liquid crystal formed by a chiral discotic mesogen

Vallerien, S. U.; Werth, Mark T.; Kremer, Friedrich; Spiess, Hans Wolfgang

doi:10.1080/02678299008047400

Cited by 56 publications

(33 citation statements)

References 17 publications

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“…In spite of their high degree of positional order in the plastic crystal phase, these systems show a temperature dependent primary relaxation time that obeys the Vogel-Fulcher-Tamman (VFT) law which is characteristic for glass forming systems [7][8][9]. 2 H NMR and dielectric spectroscopy studies on triphenylene derivatives revealed that the glass transition is related to the hindered rotation of rotationally disordered discs around their columnar axis and is not coupled with the side chain mobility [5,10,11]. For another hexasubstituted triphenylene derivative, where one of the side chains is a chloroester, it was found that the glass transition is highly anisotropic, having a much more pronounced effect along the columnar axis [6].…”

Section: Introductionmentioning

confidence: 97%

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Yildirim

Wübbenhorst

Mendes

et al. 2005

Journal of Non-Crystalline Solids

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The dynamics and phase behavior of the discotic liquid crystalline compound hexahexyloxytriphenylene (HAT6) and a derivative were studied by broad-band dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction and optical microscopy. While the pristine compound HAT6 forms both a columnar mesophase (Col h ) and a plastic crystal phase, no liquid crystallinity was observed for the highly asymmetric compound HAT6-C 10 Br. This paper focuses on the dielectric relaxations in the plastic crystal phase. For HAT6-C 10 Br, a Ôhigh temperatureÕ glass transition, manifested by a Vogel-Fulcher-Tammann (VFT) type a 2 -process, was found at À31°C that was assigned to the columnar glass transition in accordance with previous literature. The main result of our study is the observation of a second, low-temperature VFT process (a 1 ) for both compounds, which indicates co-operative liquid dynamics within the framework of the plastic crystal order at temperatures as low as À100°C. Comparison of these fast dynamics with relaxation data from polyethylene and polymer series with long alkyl groups identifies this process as a ÔhinderedÕ polyethylene-like dynamic glass transition that originates from the nanophase-separated, spatially confined fraction of aliphatic tails.

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Section: Introductionmentioning

confidence: 97%

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Yildirim

Wübbenhorst

Mendes

et al. 2005

Journal of Non-Crystalline Solids

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“…We columnar structure. Dielectric studies, for both chiral think that in our case the same explanation is possible [14,15 ] and achiral [16] discogens forming columnar if a helical structure, consisting of tilted molecules whose non-tilted mesophases, also show these two modes. In tilt direction rotates along the columnar axis, is present these studies, the respective compounds showed a glass (see ® gure 1).…”

Section: Gonal (Ordered or Disordered) Lattice In The Plane Normalmentioning

confidence: 79%

Dielectric study of the tilted columnar mesophase in three new chiral metallorganic discotic mesogens

Palacios¹,

Fuente²,

Jubindo³

et al. 1998

Liquid Crystals

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Chiral oxovanadium ( IV), copper (II) and palladium (II) b-diketonates show a room temperature tilted columnar mesophase (rectangular P21 ). The dielectric response of these compounds was measured in the frequency range 10Õ 2 ± 10 9 Hz. Three di erent relaxation processes have been observed in the columnar phase. One of them is only present in this mesophase and we suggest that it is a Goldstone-like mode, similar to the one present in the helical SmC* phases. In our case the presence of the helix was con® rmed by circular dichroism studies.

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“…The free volume outside the triphenylene core was reduced by asymmetrically substituting relatively large size groups as one of the six side arms, thereby reducing the associated free volume and destroying the symmetry of the molecule as well. By combining 2 H NMR [27] and dielectric spectroscopy [28], it was shown that the glass transition of such columnar discotic phases is connected with the prevention of crystallization. However, this is also analogous to the result of the freezing of the rotational motions of the side arms thereby inducing rotation of the disc-like molecules about the columnar axis.…”

Section: Resultsmentioning

confidence: 99%

Modification of DOBOB mesogen

Zeng

Jacob

Polk

2004

Polymer

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Molecular dynamics and the glass transition in a columnar liquid crystal formed by a chiral discotic mesogen

Cited by 56 publications

References 17 publications

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Dielectric study of the tilted columnar mesophase in three new chiral metallorganic discotic mesogens

Modification of DOBOB mesogen

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